1. Field of the Invention
This invention relates to a method and apparatus for displaying a three dimensional object, and more particularly, to a method and apparatus suitable for displaying a sphere, a column and the like on a display screen.
2. Description of Related Arts
In conventional graphics system for displaying images of objects in three dimensions, filling and displaying of the various three dimensional objects are performed by dividing a surface of each three dimensional object to be displayed into a plurality of triangles or quadrilaterals, obtaining color data for every pixel through applying luminance calculation for each divided figure, then filling and displaying each divided figure based on the obtained color data. Display with reality can be accordingly performed by taking each light source vector (a vector starting from a reflecting point and directed to a light source) and each view point vector (a vector starting from a reflecting point and directed to a view point) into consideration, regardless of the species of the three dimensional object. However, a disadvantage of a remarkable increase in the necessary time period between starting operations and visually displaying a three dimensional object, has arisen. This is caused by the fact that a three dimensional object should be divided into a great many triangles or quadrilaterals when the quality of the displayed three dimensional object is to be improved, thereby resulting in greatly increasing the amount of operations and processings.
When the three dimensional object to be displayed is a sphere, the display is scarcely changed even when each light source vector and view point vector are greatly varied. But the same operations and processings as the above-mentioned operations and processings, are needed for every sphere to be displayed, thereby resulting in lengthening the time period for display beyond that which is necessary. Also, when a three dimensional object to be displayed is a column, the display is changed little even when each light source vector and view point vector are greatly varied. But the same operations and processings as the above-mentioned operations and processings, are needed for every column to be displayed, thereby resulting in lengthening the time period for display beyond that which is necessary. The similar disadvantage has arisen when a three dimensional object to be displayed is not a sphere or a column and is not greatly changed even when a light source vectors and a view point vectors vary.
To be more specific, when a three dimensional object is a free shape, the repeated display of the three dimensional object in a graphics system for displaying images of objects in three dimensions, in general is not of great concern. As a result, the above-mentioned disadvantage is not widely recognized. However, in certain situations a sphere, a column and the like are necessary, for example, in displaying of chemical molecular structure used in molecular design. Where a great many spheres and columns are frequently and repetitively displayed on the same screen is one of those situations. As a result, the above-mentioned disadvantage is recognized as a problem.